Theoretical Physics

Theoretical simulations of spin-flip transition in Invar alloys

In 1897 C.-E. Guillaume discovered that fcc Fe-Ni alloys with a Ni concentration around 35 atomic % exhibit anomalously low, almost zero, thermal expansion over a considerable temperature range. This effect, also known as the Invar effect, is widely used in instruments, for example, as hair springs in watches. The discovery was awarded the Nobel Prize in Physics. Yet, though it has been more than 100 years since this effect was discovered, it is not fully understood.
Recently, we suggested that the Invar anomaly is related to a magnetic phase transition from the ordered ferromagnetic state at high volumes to increasingly disordered noncollinear magnetic state at lower volumes (Nature 400, 46 (1999)). Within this project you will simulate the original stage of this transition, that is a spin flip transition at Fe atoms in the alloy with predominantly Fe nearest neighbors. A dependence of the transition volume on the alloy composition, as well as a competition of the spin-flip state with other magnetic states in the alloy are of interest.